Are you looking to do a pure run, or are you headed to DTW/TOL anyway? If the latter, the more restrictive tickets that require more than a night's stay may work you. For instance, fare basis VL14M77N ($142) looks like it allows you to route NYC-IAD-somewhere such as PHL/PIT/RIC/CLE-ORD-DTW. You should net around 4k base miles/8 segments for the trip.

Go to Expedia and choose Airline Fare List. Search your starting and ending airport, and then look at the rules for the fare you want. At the bottom it'll show you the allowable routing.

I've found that majongguy's FFAssist is a great tool for playing around with routings for mileage runs on UA.